Genotipificacion del gen HLA DQB1 en diabetes autoinmune del adulto ( LADA ) / HLA DQB1 genotyping in latent autoimmune diabetes of adults ( LADA )

La diabetes autoinmune es una enfermedad multifactorial causada por factores genéticos predisponentes y ambientales desencadenantes. Se manifiesta en la edad infantojuvenil (diabetes tipo 1, DMID) y en la edad adulta (diabetes autoinmune latente del adulto, LADA). La predisposición genética es de tipo poligénico, se ha establecido asociación con alelos polimórficos del gen DQB del sistema HLA, VNTR del gen de insulina y polimorfismos en el gen CTLA4. En el presente trabajo se analizaron las frecuencias de los alelos polimórficos del gen HLA DQB1 en 63 pacientes LADA, 70 pacientes DMID y 79 individuos normales. La tipificación de los alelos del gen DQB1 se llevó a cabo mediante el Kit SSPTM DQ Olerup. Se observó una mayor frecuencia del genotipo *0201-*0302 y *0201-*0201 en ambas poblaciones diabéticas con respecto a normales (p<0.05). La presencia del genotipo *0201-*0302 fue mayor en DMID que en LADA (p<0.05). Por otra parte, el análisis del alelo protector *0602 muestra una alta prevalencia en individuos normales con respecto a la población diabética. El alelo de susceptibilidad más frecuente en pacientes LADA y DMID de nuestro país fue el *0201. En conclusión, LADA presenta susceptibilidad genética dada por alelos del gen HLA DQB1 pero en forma menos determinante que en diabetes tipo 1. A su vez, el hallazgo del aumento en la frecuencia del alelo *0201, tanto en frecuencias alélicas como genotípicas permite caracterizar nuestra población de pacientes tanto LADA como DMID a diferencia de otras poblaciones en las que el alelo más frecuente es el *0302. (AU)

Genotipificacion del gen HLA DQB1 en diabetes autoinmune del adulto ( LADA ) / HLA DQB1 genotyping in latent autoimmune diabetes of adults ( LADA )

La diabetes autoinmune es una enfermedad multifactorial causada por factores genéticos predisponentes y ambientales desencadenantes. Se manifiesta en la edad infantojuvenil (diabetes tipo 1, DMID) y en la edad adulta (diabetes autoinmune latente del adulto, LADA). La predisposición genética es de tipo poligénico, se ha establecido asociación con alelos polimórficos del gen DQB del sistema HLA, VNTR del gen de insulina y polimorfismos en el gen CTLA4. En el presente trabajo se analizaron las frecuencias de los alelos polimórficos del gen HLA DQB1 en 63 pacientes LADA, 70 pacientes DMID y 79 individuos normales. La tipificación de los alelos del gen DQB1 se llevó a cabo mediante el Kit SSPTM DQ Olerup. Se observó una mayor frecuencia del genotipo *0201-*0302 y *0201-*0201 en ambas poblaciones diabéticas con respecto a normales (p<0.05). La presencia del genotipo *0201-*0302 fue mayor en DMID que en LADA (p<0.05). Por otra parte, el análisis del alelo protector *0602 muestra una alta prevalencia en individuos normales con respecto a la población diabética. El alelo de susceptibilidad más frecuente en pacientes LADA y DMID de nuestro país fue el *0201. En conclusión, LADA presenta susceptibilidad genética dada por alelos del gen HLA DQB1 pero en forma menos determinante que en diabetes tipo 1. A su vez, el hallazgo del aumento en la frecuencia del alelo *0201, tanto en frecuencias alélicas como genotípicas permite caracterizar nuestra población de pacientes tanto LADA como DMID a diferencia de otras poblaciones en las que el alelo más frecuente es el *0302.

A 138-nucleotide deletion in the thyroglobulin ribonucleic acid messenger in a congenital goiter with defective thyroglobulin synthesis.

Two siblings (HSN and AcSN) with congenital goitrous hypothyroidism were investigated in terms of clinical, biochemical, and molecular biology. Diagnosis of defective thyroglobulin (Tg) was based on findings of low serum T4, low normal or normal serum T3, a negative percholate discharge test, and the virtual absence of the serum Tg response to challenge by bovine TSH. Only minute amounts of Tg-related antigens were detected by RIA in the goitrous tissue (HSN, 0.82 mg/g, compared to 70-90 mg/g in normal thyroid tissue), as confirmed by sodium dodecyl sulfate-agarose gel electrophoresis that indicated the virtual absence of Tg. The Tg messenger ribonucleic acids (mRNAs) from controls and HSN thyroid tissue were first reverse transcribed and then divided into several portions from positions 57-8448; the resulting complementary DNAs were, in turn, amplified by reverse polymerase chain reaction. The amplification of nucleotides 5165-6048 from control thyroid tissue Tg mRNA showed a fragment of 884 base pairs (bp). In contrast, the fragment present in the HSN was +/- 750 bp and lacked the normal fragment. The sequencing of the smaller fragment revealed that 138 bp were missing between positions 5590-5727 of the HSN Tg mRNA. This deletion does not affect the reading frame of the resulting mRNA and is potentially fully translatable into a Tg polypeptide chain that is shorter by 46 residues. A cysteine residue is maintained by the junction between the proximal T from leucine 1831 and the distal GT from cysteine 1877. DNA genomic polymerase chain reaction amplification excludes a deletion in the Tg gene and indicates that the deleted 138-nucleotide sequences lie in the same exon. The functional consequences of the deletion are not entirely clear, but it is conceivable that the excision of this segment of the Tg molecule could affect the protein structure, resulting in its premature degradation, very low colloid storage, and diminished thyroid hormone production rate.

Molecular genetics of hereditary thyroid diseases due to a defect in the thyroglobulin or thyroperoxidase synthesis.

1. Hereditary goiter and the various degrees of thyroid hypofunction are the result of structural changes in the thyroglobulin (Tg) or thyroperoxidase (TPO) proteins, the inability to couple iodotyrosines or defective iodination, impairing or substantially altering the synthesis of T4 and T3. 2. The first mutations in the Tg and TPO genes responsible for human cases of dyshormonogenesis have been described. The mutation in two siblings with hereditary goiter and marked impairment of Tg synthesis was a cytosine to thymine transition creating a stop codon at position 1510. The point mutation is removed by the preferential accumulation of a 171-nt deleted Tg mRNA. In another subject, molecular studies revealed that exon 4 was missing from the major Tg transcript due to a cytosine to guanine transversion at position minus 3 in the acceptor splice site of intron 3. 3. Genomic DNA studies identified a duplication of a 4-base sequence in the eighth exon of the TPO gene. Interestingly, besides abolishing the enzymatic activity by disrupting the reading frame of the messenger RNA and introducing stop codons, the GGCC duplication also unmasks a cryptic acceptor splice site in exon 9. 4. In conclusion, the identification of different molecular defects provided evidence that hereditary goiter associated with abnormal Tg or TPO synthesis is caused by heterogeneous genetic alterations.

Molecular genetics of hereditary thyroid disease due to a defect in the thyroglobulin or thyroperoxidase synthesis

1. Hereditary goiter and the various degrees of thyroid hypofunction are the result of structural changes in the thyroglobulin (Tg) or thyroperoxidase (TPO) proteins, the inability to couple iodotyrosines or defective iodination, impairing or substantially altering the synthesis of T4 and T3. 2. The first nmutations in the Tg and TPO genes responsable for human cases of dys-hormonogenesis have been described. The mutation in two siblings with hereditary goiter and marked impairment of Tg synthesis was a cytosine to thymine transition creating a stop codon at postion 1510. The point mutation is removed by the preferential accumulation of a 171-nt deleted Tg mRNA. In another subject, molecular studies revealed that exon 4 was missing from the major Tg transcript due to a cytosine to guanine transversion at postion minus 3 in the acceptor splice site of intron 3. 3. Genomic DNA studies identified a duplication of a 4-base sequence in the eight exon of the TPO gene. Interestingly, besides abolishing the enzymatic activity by disrupting the reading frame of the messenger RNA and introducing stop codons, the GGCC duplication also unmasks a cryptic acceptor splice site in exon 9. 4. In conclusion, the identification of different molecular defects provied evidence that hereditary goiter associated with abnormal Tg or TPO synthesis is caused by heterogeneous genetic alterations